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Effects of vitamin D and calcium supplementation on pancreatic β cell function, insulin sensitivity, and glycemia in adults at high risk of diabetes: the Calcium and Vitamin D for Diabetes Mellitus (CaDDM) randomized controlled trial

Mitri, Joanna, Dawson-Hughes, Bess, Hu, Frank B., Pittas, Anastassios G.
The American journal of clinical nutrition 2011 v.94 no.2 pp. 486-494
adults, blood glucose, body mass index, calcium, calcium carbonate, glucose, glycohemoglobin, insulin, insulin resistance, insulin secretion, noninsulin-dependent diabetes mellitus, observational studies, risk, vitamin D
BACKGROUND: A suboptimal vitamin D and calcium status has been associated with higher risk of type 2 diabetes in observational studies, but evidence from trials is lacking. OBJECTIVE: We determined whether vitamin D supplementation, with or without calcium, improved glucose homeostasis in adults at high risk of diabetes. DESIGN: Ninety-two adults were randomly assigned in a 2-by-2 factorial-design, double-masked, placebo-controlled trial to receive either cholecalciferol (2000 IU once daily) or calcium carbonate (400 mg twice daily) for 16 wk. The primary outcome was the change in pancreatic β cell function as measured by the disposition index after an intravenous-glucose-tolerance test. Other outcomes were acute insulin response, insulin sensitivity, and measures of glycemia. RESULTS: Participants had a mean age of 57 y, a body mass index (BMI; in kg/m²) of 32, and glycated hemoglobin (Hb A₁c) of 5.9%. There was no significant vitamin D x calcium interaction on any outcomes. The disposition index increased in the vitamin D group and decreased in the no-vitamin D group (adjusted mean change ± SE: 300 ± 130 compared with -126 ± 127, respectively; P = 0.011), which was explained by an improvement in insulin secretion (62 ± 39 compared with -36 ± 37 mU · L⁻¹ · min, respectively; P = 0.046). Hb A₁c increased less, but nonsignificantly, in the vitamin D group than in the no-vitamin D group (0.06 ± 0.03% compared with 0.14 ± 0.03%, respectively; P = 0.081). There was no significant difference in any outcomes with calcium compared with no calcium. CONCLUSION: In adults at risk of type 2 diabetes, short-term supplementation with cholecalciferol improved β cell function and had a marginal effect on attenuating the rise in Hb A₁c. This trial was registered at as NCT00436475.